High speed voiceband data transmission and reception
First Claim
1. An apparatus for receiving information through a medium which has a bandwidth substantially the same as the voiceband, said information having been encoded in the form of a signal whose duration is a function of the information, said apparatus comprising:
- means for detecting two consecutive instances when the amplitude of the signal received crosses a predetermined threshold level;
means for determining the information from the time duration between the two instances;
wherein the information received by the apparatus is in the form of a digital word and originates from a source which includes a clock operated at a predetermined rate and wherein the signal pulse transmitted by the source is generated with a duration proportional to the digital word divided by the rate of the clock, and wherein the determining means converts the duration of the signal pulse received back into the digital word, said determining means including;
counter means operated at substantially the same rate as the clock of the source; and
means for controlling the counting of the counter means so that the controlling means starts the counter means upon detecting the rising leading edge of the signal pulse and stops the counter means when the counter means has counted for a time duration substantially equal to the duration of the signal pulse form the source received by the apparatus, wherein the count of the counter means when counting stops is substantially the same as the digital word at the source.
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Abstract
ASCII characters are coded in the form of 8, 16 or longer digital words. Signal pulses with durations proportional to such digital words are generated and filtered so that the filtered signal has substantially the same duration as the unfiltered signal. The filtered signal fits within the voiceband so that it can be transmitted through a voiceband medium such as a telephone network. At the receiver, zero-crossings of the received signal are detected and from the duration between consecutive zero-crossings, the particular ASCII represented by the duration of such signal may be recovered.
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Citations
14 Claims
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1. An apparatus for receiving information through a medium which has a bandwidth substantially the same as the voiceband, said information having been encoded in the form of a signal whose duration is a function of the information, said apparatus comprising:
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means for detecting two consecutive instances when the amplitude of the signal received crosses a predetermined threshold level; means for determining the information from the time duration between the two instances; wherein the information received by the apparatus is in the form of a digital word and originates from a source which includes a clock operated at a predetermined rate and wherein the signal pulse transmitted by the source is generated with a duration proportional to the digital word divided by the rate of the clock, and wherein the determining means converts the duration of the signal pulse received back into the digital word, said determining means including; counter means operated at substantially the same rate as the clock of the source; and means for controlling the counting of the counter means so that the controlling means starts the counter means upon detecting the rising leading edge of the signal pulse and stops the counter means when the counter means has counted for a time duration substantially equal to the duration of the signal pulse form the source received by the apparatus, wherein the count of the counter means when counting stops is substantially the same as the digital word at the source. - View Dependent Claims (2, 3, 4)
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5. A modem for modulating information from an information store for transmission through a medium which has a bandwidth substantially the same as the voiceband and for demodulating signals received from the medium to recover information contained therein destined for the information store, said modem comprising:
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(a) a transmitting portion comprising; means for generating a signal pulse whose duration is a function of the information from the information store to be transmitted; filter means for filtering the signal pulse so that the duration of the filtered signal is substantially the same as that the signal pulse; means for transmitting the filtered signal through the medium; and (b) a receiving portion comprising; means for detecting two consecutive instances when the amplitude of the signal receiver crosses a predetermined threshold level; means for determining the information from the time duration between the two instances an for transmitting the information to the information store. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for receiving information by means of a receiver from a transmitter through a medium which has a bandwidth substantially the same as the voiceband, said information having been encoded in the form of a signal whose duration is a function of the information, wherein the transmitter transmits the information a second time in the form of a second signal, said method comprising:
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detecting two consecutive instances when the amplitude of the signal received crosses a predetermined threshold level; determining the information from the time duration between the two instances; storing the time duration; detecting two consecutive instances when the amplitude of the second signal received crosses a predetermined threshold level; determining the information from the second time duration between the two instances when the amplitude of the second signal crosses the threshold level; and comparing the first and second time durations and generating a re-send signal for transmission to the transmitter requesting the transmitter to re-send the information when the two time durations compared are different.
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Specification